In general, a semiconductor device having a deep impurity layer is known. For example, a pixel isolation layer in a CMOS sensor and a well layer in a CCD sensor are impurity layers that need to be formed at least deeper than a photoelectric conversion section.
The deep impurity layers such as the pixel isolation layer and the well layer, etc. are formed by plural times of ion implantations while changing an acceleration voltage of ions, and thereby creating a plurality of density peaks in a depth direction. Alternatively, it may be formed by diffusing the ions in the depth direction by a thermal diffusion over a long period of time after having performed the ion implantation once.
As aforementioned, conventionally, it is difficult to form such a deep impurity layer in a short period of time since the deep impurity layer has been formed by the plural times of the ion implantation steps or the time-consuming thermal diffusion step. Accordingly, in a case of a solid-state imaging device such as the CMOS sensor, the CCD sensor, etc., a long period of time is required to form the pixel isolation layer or the well layer, and this has been a cause of an obstruction to an improvement of a throughput in producing the solid-state imaging device.
It is one of the objects of an embodiment of the present invention to provide a method for forming a deep impurity layer extending from a surface toward a depth direction can be formed in a short period of time, to provide an exposure mask therefore and to provide a method for producing a solid-state imaging device by which a throughput can be improved.